Kernel subsampling for an accelerated tree similarity computation

Approaches herein relate to machine learning for detection of anomalous logic syntax. Herein is acceleration for comparison of parse trees such as suspicious database queries. In an embodiment, a computer identifies subtrees in each of many trees. A respective subset of participating subtrees is selected in each tree. A respective root node of each participating subtree should directly have a child node that is a leaf and/or should have a degree that exceeds a branching threshold such as one. For each pairing of a respective first tree with a respective second tree, based on a count of subtree matches between the participating subset of subtrees in the first tree and the participating subset of subtrees in the second tree, a respective tree similarity score is calculated. A machine learning model inferences based on the tree similarity scores of the many trees. In an embodiment, each tree similarity score is a convolution kernel.